The purpose of this trial is to evaluate the role of calcium supplementation in the prevention of preeclampsia and pre-term delivery. The protocol involved a randomized double-blind placebo controlled trial in 900 nulliparous pregnant women. Two grams of calcium carbonate or placebo were given per day beginning by week 21 and patients were followed prospectively for endpoints such as pregnancy aggravated hypertension, pregnancy aggravated proteinuria, preeclampsia and urolithiasis. This study has been completed and the data is in analysis.